This invention relates to a balanced, single cover elastic yarn and to a novel method of making the yarn. More particularly, the invention relates to a yarn in which an elastic core is helically wrapped with a thermoplastic strand, and stresses in the thermoplastic strand are relieved by heat application.
Elastic yarns usually consist of an elastic core about which is helically wrapped one or more strands of material. Normally, such elastic yarns are formed by directing an inelastic strand about an elastic core or filament resulting in a single cover elastic yarn, or by directing two equal inelastic strands about an elastic core in opposite directions resulting in a double covered yarn, which is normally balanced. The cover strand or strands are wrapped or directed about the elastic core when the core is stretched, thus maintaining the core under tension and preventing contraction of the core to its original size. The elastic core may or not have twist therein, and the cover strand or strands may have twist therein prior to the being helically wrapped about the core, or the cover material may be relatively untwisted before being wrapped about the core. The core or elastic filament may be spandex, rubber or the like while the cover strands may be of various natural or synthetic textile fibers or filaments, particularly themoplastic materials.
Single cover, balanced elastic yarns are well known, as taught by U.S. Pat. Nos. 2,061,021; 2,804,745; 3,098,347; and 2,690,047.
Single cover elastic yarns generally are not used in the leg portions of pantyhose garments due to poor and inadequate cover of the elastic core because of the low number of wraps per inch of the cover strand upon the core. Also, merely increasing the number of wraps per inch further restricts the stretch characteristics of the elastic core. Further, increasing the number of wraps per inch of the cover strand is not satisfactory since the resultant elastic yarn is more torque lively and difficult to knit. Because of this tendency to kink or curl, such elastic yarns are difficult to control during knitting and fabric produced is inferior in quality.
In the processing of elastic yarns, particularly knitting of hosiery goods, the yarns must present a good appearance, have satisfactory stretch characteristics, and be free of any tendency to twist or kink during knitting.
Generally, man made yarns sold today have little or no twist therein, that is, a twist of 0.5 to 2.5 turns per inch. In the past, balanced single cover elastic yarns have been produced by various means. In U.S. Pat. No. 2,804,745, a core is pretwisted in one direction and a cover wrapped about the core in the opposite direction such that the cover and core counter-balance. As disclosed in U.S. Pat. No. 3,098,347, both the cover and core are pretwisted and both twists are removed as the cover is wrapped about the core. U.S. Pat. No. 2,061,021 discloses wrapping a cover yarn about an untwisted core to produce an unbalanced elastic yarn. In order to balance the elastic yarn, the elastic yarn is withdrawn from the driven package removing some spiral wraps from the cover and at the same time imparting a reverse twist to the core.
In many prior processes, it was necessary to pre-twist the elastic core to a very great extent to obtain a balanced yarn. However, pre-twisting of the core is costly and the degree of stretch is limited as the pre-twist of the core increases, thus restricting the ultimate extensibility of the final elastic yarn.
In accordance with the present invention, a twist is applied to the elastic core as it is removed from a supply source and the elongation or draft of the core is positively controlled within a zone intermediate the supply and a yarn take-up apparatus. The inelastic cover is helically wrapped about the core while the core is in a controlled, extended condition. The elastic yarn is permitted to relax or at least partially contract and is wound upon the take-up apparatus in a somewhat balanced state. The resultant yarn then is subjected to heat to relax or relieve the stresses in the cover strand to balance the yarn in the relaxed state.
One of the primary objects of the invention is the provision of a new and improved method for producing single cover elastic yarn balanced in the relaxed state.
Another object of the invention is the provision of a method for producing a more uniform single cover elastic yarn having a more complete coverage of the core.
Still another object of the invention is the provision of a system for producing a single cover elastic yarn which is balanced and torque free in the relaxed condition.
A further object of the invention is the method of producing an uniform, well-covered core having a greater range of elongation with a given number of wraps per inch of the single cover yarn.
Other objects and advantages of the invention will become apparent when considered in view of the following detailed description.